U.S. patent application number 12/094409 was filed with the patent office on 2008-10-23 for detection module.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS, N.V.. Invention is credited to Jacobus Josephus Leijssen, Harry Marinus.
Application Number | 20080258048 12/094409 |
Document ID | / |
Family ID | 38049043 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080258048 |
Kind Code |
A1 |
Leijssen; Jacobus Josephus ;
et al. |
October 23, 2008 |
Detection Module
Abstract
A detection module for detecting electro-magnetic radiation
comprises a photosensor, a current integration circuit and an
arithmetic unit fits the integration samples to a predetermined
time dependency of the integrated current and computes an
accumulated electrical charge accumulated over the integration time
interval from the fit. Notably, the detection module is employed in
an optical imaging apparatus to image e.g. a woman's breast by way
of near-infrared light.
Inventors: |
Leijssen; Jacobus Josephus;
(Eindhoven, NL) ; Marinus; Harry; (Eindhoven,
NL) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS,
N.V.
EINDHOVEN
NL
|
Family ID: |
38049043 |
Appl. No.: |
12/094409 |
Filed: |
November 9, 2006 |
PCT Filed: |
November 9, 2006 |
PCT NO: |
PCT/IB2006/054177 |
371 Date: |
May 21, 2008 |
Current U.S.
Class: |
250/214L ;
250/214R |
Current CPC
Class: |
A61B 5/0091 20130101;
A61B 5/4312 20130101 |
Class at
Publication: |
250/214.L ;
250/214.R |
International
Class: |
G01J 1/44 20060101
G01J001/44 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 21, 2005 |
EP |
05111000.5 |
Claims
1. A detection module for detecting electro-magnetic radiation
comprising a photosensor to derive an electrical current from
incident electro-magnetic radiation a current integration circuit
to (i) integrate the electrical current from the photosensor over
an integration time interval and (ii) to acquire several
integration samples of time-integrated current during the
integration time interval and an arithmetic unit to (i) fit the
integration samples to a predetermined time dependency of the
integrated current (ii) compute an accumulated electrical charge
accumulated over the integration time interval from the fit and
(iii) supply an output intensity signal that represents the
accumulated electrical charge.
2. A detection module as claimed in claim 1, further comprising a
synchronisation circuit to (i) receive a monitor signal that is
representative of a disturbance from a disturbance source and (ii)
control the operation of the detection module circuit to form the
output intensity signal on the basis of the monitor signal.
3. A detection module as claimed in claim 1, wherein the
predetermined time dependency of the integrated current is
linear.
4. A detection module as claimed in claim 1, wherein the current
integration circuit is arranged to acquire a number of integration
samples in the range of 400-500 samples.
5. A detection module as claimed in claim 1, wherein the current
integration circuit is arranged to acquire the integration samples
at a temporal density of samples/second in the range (low
high).
6. An apparatus for imaging a turbid medium comprising an
examination space to receive the turbid medium one or more
detection modules as defined in claim 1 placed near the examination
space to detect electromagnetic radiation from the turbid medium
and the detection module(s) being arranged to supply the output
intensity signals that a reconstruction module to receive the
output intensity signals from the detection module(s) and
reconstruct an image of the turbid medium from the output intensity
signals.
7. A method of detection of electro-magnetic radiation comprising
the steps of deriving an electrical current from incident
electro-magnetic radiation integrate the electrical current over an
integration time interval and acquire several integration samples
of time-integrated current during the integration time interval and
fit the integration samples to a predetermined time dependency of
the time-integrated electrical current compute an accumulated
electrical charge accumulated over the integration time interval
from the fit and supply an output intensity signal that represents
the accumulated electrical charge.
8. A method of detection of electro-magnetic radiation wherein (i)
a monitor signal is received that is representative of a phase of a
disturbance source and (ii) the current integration circuit to
integrate the electrical current is controlled on the basis of the
monitor signal.
9. A computer programme comprising instructions to acquire several
integration samples of time-integrated current during an
integration time interval fit the integration samples to a
predetermined time dependency of the time-integrated electrical
current and compute an accumulated electrical charge accumulated
over the integration time interval from the fit.
Description
[0001] The invention pertains to a detection module for the
detection of electro-magnetic radiation which comprises a
photosensor with a current integration circuit. The invention also
pertains to an apparatus for imaging a turbid medium.
[0002] The international application WO2003/077724 shows an optical
tomographic scanning apparatus with a detector system.
[0003] The known optical tomographic scanning apparatus is designed
to image a woman's breast. Accordingly the known optical
tomographic scanning apparatus forms an apparatus for imaging a
turbid medium formed by the breast tissue. The known optical
tomographic scanning apparatus is provided with an near-infrared
(nir) laser to illuminate the woman's breast to be examined. A
detector system is orbited around the breast to detect nir-light
transmitted through and re-emitted by the breast from several
angular positions in the orbit. The detector system is provided
with a photodiode to convert the incident light into an electrical
output current. This known detector system integrates the output
electrical current from the photodiode successively at several
different integration intervals of successively longer lengths.
Then, the values obtained at the end of the respective integration
intervals are digitised. This approach amounts to oversampling or
multiple sampling by repeatedly digitising the output electrical
current from the photodiode. These multiple samplings are averaged
to improve the signal-to-noise ratio of the averaged signal. In the
averaged signal quantisation errors are reduced. Such quantisation
errors have the effect that is like additive noise.
[0004] An object of the invention is to provide a detection module
for detection of electromagnetic radiation of which the output has
a high signal-to-noise ratio especially at low intensities of the
incident electro-magnetic radiation. Also an object of the
invention is provide a detection module for detection of
electromagnetic radiation which does not require long signal
acquisition and/or signal processing time.
[0005] This object is achieved by the detection module for
detecting electro-magnetic radiation of the invention which
comprises
[0006] a photosensor to derive an electrical current from incident
electro-magnetic radiation
[0007] a current integration circuit to
[0008] (i) integrate the electrical current from the photosensor
over an integration time interval and
[0009] (ii) to acquire several integration samples of
time-integrated current during the integration time interval
and
[0010] an arithmetic unit to
[0011] (i) fit the integration samples to a predetermined time
dependency of the integrated current
[0012] (ii) compute an accumulated electrical charge accumulated
over the integration time interval from the fit and
[0013] (iii) supply an output intensity signal that represents the
accumulated electrical charge.
[0014] The detection module to detect electro-magnetic radiation of
the invention takes multiple samples of the time-integrated
electrical current from the photosensor. Thus the detection module
by way of its current integration circuit tracks the accumulation
of electrical charge are electrical current is being integrated
over the integration time interval. These multiple samples are fit
to the predetermined time dependency of the time-integrated
electrical current. This predetermined time dependency is
determined by the design of the photosensor and the time-dependency
of the intensity of the incident radiation. On the basis of this
information the predetermined time dependency of the
time-integrated electrical current can be modelled in the form of a
parameterised mathematical function. Thus, a mathematical model is
provided that accurately represents the actual values of the time
dependent time-integrated current as the integration time interval
progresses. In many practical situations the intensity of the
incident is about constant over the integration time interval. This
situation notably occurs when the integration time interval is much
shorter than the typical time scale of the variation of the
intensity of the incident electro-magnetic radiation. For example,
a linear approximation has provide accurate results for an
integration interval having a time length of 10-100 ms. On the
other hand, when the temporal variation of the intensity of the
incident electro-magnetic radiation is predetermined or can be
accurately estimated, the time-dependence of the intensity can be
included in the mathematical model. The actual details of the
mathematical function, i.e. one or several of its parameters are
obtained by applying a fit procedure on the basis of the
predetermined time dependency to the sampled values. Then the
accurate value of the time-integrated electrical current as
accumulated over the integration time interval is simply computed
as the value of the actual time-dependency from the fit at the end
point of the integration time interval. The fit procedure
suppresses errors due to electronic noise, photon shot noise and
digitisation errors and the like, since the entire accumulation of
electrical current as the integration time interval progresses is
taken into account. Notably, the fit procedure takes into account a
substantial part of the accumulation of electrical current during
the integration time interval, rather than just relying on the
accumulated value sampled at the end point of the integration time
interval. Experiments have shown that the detection module of the
invention actually achieves a very low noise floor of less than 10
fA (10.10.sup.-15A). Accordingly, the detection module of the
invention is able to accurately measure very low electrical
currents of less than 25 fA with a good signal-to-noise ratio. For
example a root-mean-square (rms) noise of less than a fA (i.e.
below 10.sup.-15A)is achieved. Notably, noise in the integrated
electrical current is amplified by impedance gain due to an
operational amplifier that is employed in the current integration
circuit. The present invention by way of the fit to linear increase
with time of the integrated electrical current eliminates or
effectively reduces this noise. Additionally the invention reduces
the effect of variations in offset which may be caused by
electrical drift in the current integration circuit and due to
variations in electrical charge left behind after resetting a
collecting capacitor of the current integration circuit . Also
offset variations may be connected with variations of dark current
in the photosensor, and dependencies upon the offset voltage over
the photosensor.
[0015] Since the multiple sampling of the time-integrated
electrical current is done within one integration time interval,
there is no need to for a long measurement time and no successive
averaging is needed for an individual measurement of the
accumulated electrical charge that is representative for the
incident intensity of the electro-magnetic radiation during the
integration time interval.
[0016] According to a further aspect of the invention the detection
module is provided with a synchronisation circuit that has the
functions to monitor a disturbance source and to control or e.g.
trigger the integration of the electrical current from the
photosensor on the basis of the monitored phase of the disturbance
source. There are several examples of such disturbance sources,
notably switched mode power supplies and fields generated by a
mains power source are abundantly present and may disturb the
operation of the detection module especially when measuring
extremely low electrical currents. The synchronisation circuit is
for example especially adapted to initiate the sampling of the
time-integrated current when the disturbance is low or even absent.
In another example, the synchronisation circuit triggers the
sampling of the time-integrated current at a particular phase of
the disturbance for repeatedly detecting electro-magnetic
radiation. In another example the synchronisation circuit controls
the arithmetic circuit to perform a correction for the monitored
disturbance. It appears that especially when detecting very low
electrical current, synchronisation of the sampling further
improves the signal-to-noise ratio of the output intensity signal.
The noise level is effectively reduced into the range of 1 pA to 1
fA; even results of a very low noise level of less than 1 pA may be
achieved.
[0017] According to a particular aspect of the invention the
predetermined time-dependency of the integrated electrical current
is linear. This linear dependency is very simple and has appeared
to be quite accurately represents the time-integrated electrical
current as output from present day commercially available
photosensors. On the basis of the linear dependency the accumulated
electrical charge is easily calculated from the slope of the linear
dependency as found from the fit and the duration of the
integration time interval. Moreover, for the simple linear
dependency of the integrated current only a low amount of data
needs to be transferred to the arithmetic unit. This can be
achieved by inexpensive low power components. Moreover, no
additional signal transmission bandwidth is required to transfer
and process the simple datasets.
[0018] According to a further aspect of the invention the current
integration circuit the number of samples acquired for an
individual measurement in the range of typically 400-500 samples in
an individual integration interval.
[0019] The invention also pertains to an apparatus for imaging a
turbid medium. An example of such an apparatus is an imaging system
for optical or notably near-infrared imaging of a woman's breast.
Imaging of this kind of turbid medium, notably human biological
tissue is possible in a wavelength range of 50 nm to 1.4 .mu.m,
very good results are achieved in the wavelength range of 650-900
nm and excellent results are achieved in the range of 700-800 nm.
The choice of wavelength ranges depends on consideration of low
scatter (i.e. which increases at shorter wavelength) low absorption
(which increases at high wavelength) and the absence of particular
absorption bands due to e.g. oxygenated or non-oxygenated blood,
etc.. It has appeared that the breast tissue optically behaves as
turbid because of multiple scatter of the light that progresses
through the breast tissue. The imaging apparatus of the invention
comprises a examination space to receive the turbid medium. In
practice the examination space for example has the form of a
chamber that is open at it upper end and into which the woman's
breast be suspended from above into the opening of the chamber
while the woman is comfortably positioned face down (that is, in
prone position) over the chamber. Often a matching fluid is applied
to surround the breast suspended into the chamber to avoid strong
optical transitions at the edge of the breast. The use of the
matching fluid strongly reduced artifacts in the reconstructed
image of the breast being examined.
[0020] Electro-magnetic radiation from the breast is measured by
electro-magnetic radiation detection modules located at or near the
walls of the chamber. Alternatively, one or several
electro-magnetic radiation detection modules may orbit around the
examination space. The electro-magnetic radiation detection modules
detect electro-magnetic radiation from the examination space from
several orientations. In one aspect of the imaging apparatus the
breast may be illuminated by sources that are located around the
examination space or that orbit around the examination space in
order to irradiate the turbid medium, i.e. the woman's breast, from
several orientations. In another aspect of the imaging apparatus of
the invention a contrast agent is administered to the patient to be
examined which cause fluorescence from the breast tissue, where
notably fluorescence is enhanced in tumour tissue. For example the
fluorescence enhancement is due to increased concentration of
contrast agent that is due to preferred accumulation of contrast
agent in tumour tissue.
[0021] The imaging apparatus of the invention is provided with one
or more electro-magnetic radiation detection modules of the
invention as disclosed above. The electro-magnetic radiation
detection modules are employed in the imaging apparatus of the
invention to detector electro-magnetic radiation, notably optical
or near-infrared radiation from the turbid medium, notably the
woman's breast. These one or more electro-magnetic radiation
detection modules supply output intensity signals that represent
the accumulated electrical charges that in turn are representative
of the radiation intensities as observed from respective
orientations from the examination zone. These output intensity
signals are applied to a reconstructor which reconstructs one or
several images of the turbid medium, i.e. the woman's breast.
Several reconstructions algorithms are available for reconstructing
two-dimensional or three-dimensional image datasets.
[0022] The detection modules of the invention generate the output
intensity at a very good signal-to-noise ratio, especially at very
low intensity levels. Hence, reconstruction artifacts in the
reconstructed image are avoided so that the reconstructed image has
a high diagnostic quality in that small details with little
contrast are nevertheless rendered well visible.
[0023] These and other aspects of the invention will be further
elaborated with reference to the embodiments defined in the
dependent Claims.
[0024] These and other aspects of the invention will be elucidated
with reference to the embodiments described hereinafter and with
reference to the accompanying drawing wherein
[0025] FIG. 1 shows a schematic diagram of the apparatus for
imaging a turbid medium of the invention;
[0026] FIG. 2 shows a schematic cross-sectional drawing of the cup
with a turbid medium in the form of a breast;
[0027] FIG. 3 shows an electric circuit diagram of the detection
module of the invention for detecting electro-magnetic
radiation;
[0028] FIG. 4 shows a sampled integrated photocurrent of 16 fA
and
[0029] FIG. 5 shows results from experiments on several individual
integration intervals.
[0030] FIG. 1 shows a schematic diagram of the apparatus for
imaging a turbid medium of the invention. Notably, the apparatus
for imaging a turbid medium shown diagrammatically in FIG. 1 is an
optical mammography system. The optical mammography system
comprises a carrier 11 on which the patient to be examined (notably
a woman whose breast(s) 1 are to be examined is placed in prone
position (i.e. face down) having one breast suspended in the
examination space 2 that has to form of a measurement cup 2 (see
FIG. 2). The space between the breast 1 and the cup surface is
filled with a scattering fluid 22, which scattering properties for
example closely match the scattering properties of the average
breast so that transitions of optical properties between the breast
tissue and space outside the breast are reduced.
[0031] FIG. 2 shows a schematic cross-sectional drawing of the cup
with a breast 1.
[0032] A large number of fibres 23 (510 in total) is connected with
one end to the cup. Half of the fibres are connected to detector
modules 5 with the other end, and half of the fibres are connected
to a fibre-switch 12 with the other end. The fibre-switch 12 can
direct light from three different lasers 24 in either one of the
256 source fibres 23 (255 to the cup, one directly to a detector
fibre). In this way, either one of the source fibres 23 can provide
a conical light beam in the cup. By properly switching the
fibre-switch 12, all the source fibres will emit a conical light
beam subsequently.
[0033] The light from the selected source fibre is scattered by the
scattering fluid and the breast, and is detected by the 255
detector modules. The scattering of light in breast tissue is
strong, which means that only a limited amount of photons can
transverse the breast, compared to the reflected (or backscattered)
light. Therefore, a large dynamical range should be covered by the
detectors (about 9 orders of magnitude). Photodiodes are used as
photosensors 5 in the detector modules. The front-end detector
electronics includes of these photodiodes and an amplifier 31. The
amplification factor of the amplifier can be switched between
several values. The machine first measures at the lowest
amplification, and increases the amplification if necessary. The
detectors are controlled by a computer 14.
[0034] This computer 14 also controls the lasers, the fibre-switch,
and the pump system. The computer, cup, fibres, detectors,
fibre-switch, and the lasers are all mounted into a bed as shown in
FIG. 2.
[0035] A measurement starts with a cup 2 filled completely with the
scattering fluid 22, this is the calibration measurement. After
this calibration measurement, a breast 1 is immersed in the fluid,
and the measurement procedure is carried out again. Both the
calibration and the breast measurement consist of 255'255 detector
output intensity signals (OIS) for each of the three lasers 24.
These detector output intensity signals (OIS) can be converted into
a three dimensional image using a process called image
reconstruction. The image reconstruction of the image of the breast
from the is carried out by a reconstructor 4 that is usually
implemented in software in the computer 14. The reconstruction
process, which is based on for example an algebraic reconstruction
technique (ART) or finite element method (FEM), finds the most
likely solution to the (ill-defined) inverse problem.
[0036] FIG. 3 shows an electric circuit diagram of the detection
module of the invention for detecting electro-magnetic radiation.
The detection module includes in integrator circuit 32 that
includes an operational amplifier 31 and a capacitance 33 in
parallel. Further a reset switch R is in parallel with the
capacitance 33. The integration circuit receives the photocurrent
from the photodiode 5. The integrated photodiode current is sampled
during the integration period of for example 120 ms for about 460
times by the sampling unit 6, for example a 24-bit ADC may be
employed as the sampling unit. The integration samples from the
sampling unit are applied to the arithmetic unit which fits the
integration samples to a linear time dependence (see FIG. 4). From
the result of the at fit the output intensity signal is computed as
the value of the fitted linear dependency at the end of the
integration time interval, i.e. at 120 ms.
[0037] The fit procedure is now presented in some detail.
[0038] The linear dependency of the integrated electrical current
with time during the integration time interval is given as: y=bx+a
a=offset (don't care) and b=gradient or slope. This parameters are
computed as
{ a = ( .SIGMA. y ) ( .SIGMA. x 2 ) - ( .SIGMA. x ) ( .SIGMA. xy )
n .SIGMA. x 2 - ( .SIGMA. x ) 2 b = n .SIGMA. xy - ( .SIGMA. x ) (
.SIGMA. y ) n .SIGMA. x 2 - ( .SIGMA. x ) 2 Where stands for i = 1
n i ##EQU00001##
[0039] This calculation is done "on the fly" during each ADC sample
interrupt.
[0040] FIG. 4 shows a sampled integrated photocurrent of 16 fA. The
photocurrent is integrated and sampled 460 times during the 120 ms
integration time interval. This leads to the rather noise curve. To
this noisy curve a linear fit is drawn and the accumulated
electrical charge over the integration time interval is computed as
the value of the linear fit at the end point of the integration
time period, i.e. at 120 ms. This fit involves only two scalar
parameters namely the slope of the linear dependency and its offset
at the start of the integration time interval.
[0041] FIG. 5 shows results from experiments on several individual
integration intervals. Notably, FIG. 5 represents the several
repeats of the integration of the electrical current from the
photosensor. Each individual somewhat noisy streak represents an
individual integration. As FIG. 5 show, the offset at the beginning
of each individual integration may change. However, the fit
according to the invention to a linear time dependency reduces of
even eliminates the effect of this variation of the offset on the
computed accumulated electrical charge.
* * * * *